The dietary indoles, indole-3-carbinol (IC) and idole-3-acetonitrile (IAN), are found in vegetables associated with decreased risk of chemical carcinogenesis. Two other dietary indoles, tryptophan and indole, may modify hepatocarcinogenity. These four compounds are the most common indoles impacting humans via the diet. The two most common N-nitrosopyrrolidine (NPy), have been shown to require enzymatic oxidative activation to express their mutagenic and carcinogenic potential. We have shown that dietary indoles protect against the ability of NDMA and NPy to alkylate hepatic DNA and protein, and to protect against the ability of NDMA and NPy to alkylate hepatic DNA and protein, and to protect against hepatotoxicity; these effects are independent of indole ability to alter oxidative metabolism. The purposes of this proposal are to 1) optimize the chemoprotective effects of IC and IAN against N-nitrosamine hepato and geno toxicity; and 2) examine the mechanism of chemoprotection by the four mentioned dietary indoles. Our test systems will be the intact mouse, the isolated perfused mouse liver, and in vitro subcellular systems. We will obtain dose-response and time-response curves for toxicity and DNA damage produced by NDMA and NPy. We will then examine the dose-response and time-response ability of each of the 4 dietary indoles (introduced by gavage) to protect against nitrosamine effects. Evidence indicates that indole protection is mediated by nucleophilic metabolic intermediates generated in vivo. We have devised an assay system to quantitate the degree of nucleophilicity in both chemical or biological samples. We propose to trap the presumptive reactive nucleophiles generated from the indoles, and to identify/quantify the ultimate protective chemical species. For this we will use HPLC separation techniques in parallel with liquid scintillation counting to isolate the compounds, and mass spectrometry procedures for compound identification. Our long range objectives are 1) to identify potential dietary, environmental or pharmacological agents that could abate chemical mutagenic and carcinogenic risk in humans; 2) to elucidate the mechanisms of chemoprevention, and to understand the advantages and limitations of chemoprotective agents such as the indoles; and 3) to develop practical strategies for predicting and abating risk associated with human exposure to mutagens and carcinogens.